Silver halide emulsions and processes for preparing same



United States Patent 2,910,359 SILVER HALIDE EMULSIONS AND PROCESSES FOR PREPARING SAME Vere Mallet, Milltown, N.J., assignor to E. I. du Pont de- Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application August 28, 1957 Serial No. 680,649 Claims. (Cl. 96-87) This invention relates to photographic silver halide emulsions of improved stability and to a process of preparing the same. More particularly, it relates to such emulsions which contain water-insoluble hydroxides of cobalt, nickel and copper and to a process of preparing the same.

Many compounds are known which have a good stabilizing or antifogging action in photographic silver halide emulsions. The utility of many of these compounds, however, is severely limited by their tendency to decrease the sensitivity of dispersions of light-sensitive silver halide in water-permeable colloids. Moreover, since the amount of certain known stabilizing agents which can be added to a silver halide dispersion or emulsion without producing deleterious effects must be kept within a very small range of exceedingly low quantities, it is difiicult to control the quality of the dispersions from batch to batch.

An object of this invention is to provide photographic silver halide emulsions of uniform quality and enhanced stability to aging, particularly with respect to aging under conditions of relatively high humidity and at elevated temperatures, e.g., tropical conditions. Another object is to provide such emulsions which are optically sensitized. A further object is to provide a process for increasing the stability of photographic silver halide emul-.

sions, especially high-speed silver iodobromide emulsions, optically sensitized and not, without adversely affecting the sensitivity of the freshly prepared or coated emulsions. A still further object is to provide such a process 7 while simultaneously reducing the degree of fog produced upon aging and without adversely affecting the sensitivity of the aged emulsion layers of photographic films and papers. A still further object is to provide such a process wherein the amount of stabilizing agent added does not have to be carefully maintained within narrow ranges of very low quantities. Still further objects will be apparent from the following description of the invention.

The foregoing objects are attained and stable photographic silver halide emulsions and emulsion layers pro vided in accordance with the invention by adding to aqueous, light-sensitive silver halide emulsions a small amount of a polyvalent water-insoluble metal hydroxide of a metal taken from the group consisting of cobalt, nickel and copper.

The aforementioned metal hydroxide, especially copper hydroxide, preferablyis added to the emulsion after the completion of the digestion stage where the emulsion is brought to its optimum sensitivity prior to coating.

Various emulsion adjuvants can be added to the digested emulsion, prior to, simultaneously with, or even subse- 2,910,359 Patented Oct. 27, 19 59 emulsions. The useful agents of this type include (a) various polyoxyalkylene glycols and derivatives thereof, e.g., alkyl'ethers and fatty acid esters, and (b) condensation products of hexitol ring dehydration products with ethylene oxide or propylene oxide containing at least six oxyalkylene groups, said compounds (a) and (b) having a molecular weight, or an average molecular weight, of at least 300 to 8000 or more. Suitable compounds of these types are disclosed in U.S. Patents 2,423,549, 2,4441,389, 2,240,472, 1,970,578 and 2,400,532.

In preparing the stabilized emulsions of the invention, the Water-insoluble heavy metal hydroxide is used in very fine particle size, e.g., from 2 to 50 microns, preferably 2 to 8 microns in average particle size. droxide preferably is added from aqueous dispersion. The dispersion or suspension can be made from the pure metal hydroxide. The laboratory reagent grade that is commercially available is satisfactory.

As an exemplary procedure, a suspension of these materials is prepared by first weighing out 50 grams of the metal hydroxide and adding to this measure about /2 pound of glass beads. To this mixture is added 200 ml. of distilled water. The material is placed in a ball mill and mixed for 48 hours. The glass beads are then removed and the suspension diluted with distilled water to a convenient concentration, usually about 4 grams of the metal hydroxide per 1000 ml. of distilled water. The procedure for preparation is the same for each of the metal hydroxides.

The optimum amount of the stabilizer may vary for a given emulsion depending on the presence of emulsion adjuvants such as chemical sensitizers, optical sensitizers,

etc. The amount to be added is not critical and may vary from about 1.0 mole of cobalt, nickel or copper hydroxide per 1000 moles of silver halide to about 30 moles of the metal hydroxide per 1000 moles of silver halide. The preferred ranges are 5.4 to 6.8 moles of copper hydroxide, 3.0 to 18.0 moles of nickel hydroxide and 1.2 to 12.0 moles of cobalt hydroxide per 1000 moles of silver halide.

While the invention is useful in stabilizing various types of silver halide emulsions including silver chloride, silver bromide, silver chlorobromide and silver chloroiodobromide emulsions of pH 5.0 to 8.0 and higher, and emulsions made by admixing two or more of the foregoing, in the preferred aspect of the invention, an aqueous suspension of the finely divided metal hydroxide is thoroughly admixed with an aqueous high-speed gelatino silver iodobromide emulsion containing naturally occurring sulfur sensitizers. Silver halide emulsions containing other types of water-permeable colloid binding agents having protective colloid properties, particularly those of the reversible type, can be stabilized similarly in accordance with the invention. Among such binding agents are natural and synthetic colloids, e.g., albumimcasein, agaragar, polyvinyl alcohol and its partial ethers, esters and acetals.

The following examples will further illustrate but are not intended to limit the invention, and in the tables the amount of metal hydroxide is in parts of grams or grams per mole of silver halide, which is referred to as AgX. In these examples, the emulsions are prepared and coated in the absence of actinic radiations in amounts which would cause a significant exposure of the emulsions.

Example I A high-speed gelatino-silver iodobromide emulsion containing approximately 6.5 mole percent silver iodide and 93.5 mole percent silver bromide and having a silver halide to gelatin ratio of about 1 to 1.27 is prepared in the conventional manner. At the appropriate time during preparation, the emulsion is optically sensitized with The metal hy.

maining portion, 2.000 grams of Ni(OH) per mole of AgX is added. The resultingemulsions are thoroughly mixed by conventional agitation means and. thencoated onto a cellulose acetate film base. Samples of the film elements were then exposed in a typeIB sensitometer and developed in a developer of the following composition:

Water (52 C.) cc 750.0 N-methyl p-aminophenol hydrosulfate grams 0.8 Sodium sulfite (desiccated) r do 90.0 Hydroquinone do 1.0 Borax do 3.0 Potassium bromide do 0.1

Cold water to make 1000.0-ml.

for 7 minutes at 68 F. with the following table:

results listed in the Example I is repeated except that copper hydroxide, in a ratio of 0.533 gram per mole of silver halide, is substituted for the nickel hydroxide. were exposed and developed as described in Example I with the results given in the following table:

The film elements r Fresh 7 days, 120 F., 65% RH.

, Speed Oon- Fog Speed Con- Fog trast trast None 1,000 .54 .15 810 .51 .19 0.533 1, 000 09 1, 000 54 10 Example III A high-speed gelatino-silver iodobromide emulsion of the X-ray type containing approximately 1.5 mole percent silver iodide and 98.5 percent silver bromide is prepared in the conventional manner. The emulsion is divided into four parts which are given a normal digestion. One portion, without further treatment, is coated onto a cellulose acetate film base.

Grams N-methyl p-aminophenol hydrosulfate 3.0 Hydroquinone 9.0 Sodium sulfite (desiccated) 50.0 Potassium bromide 4.5 Potassium carbonate 50.0

Cold water to make 1.0 liter.

To a second portion 0.333 gram of Ni(OH) -H O per'mole of AgX is added. To a 4 for 5 minutes at 68 F. with the results shown in the following table:

Fresh 7 days, 120 F., 65% RH.

Ni(OH)z.H2O

Speed Con- Fog Speed Con- Fog trast trast Example IV A. high-speed gelatino-silver iodobromide emulsion of the negative type containing approximately 6.5 mole percent silver iodide and 93.5 mole percent silver bromide prepared in the conventional manner, but which has been optically sensitized with dyes is divided into two portionswhich are given a normal digestion. One portion is coated onto a cellulose acetate film base without further treatment. To the other portion a suspension of copper hydroxide, prepared as previously described, is added in the ratio of 0.667 gram of copper hydroxide per mole of AgX. The film elements .were exposed and developed as described in Example I, except that the period of development was increased to 10 minutes. The results are listed in the following table:

Fresh Speed Contrast Fog None .r

Example V Fresh 7 days, F., 65% RH.

011(OH); n trast Con- Fog trast Speed It, will be apparent from the foregoing examples that the stability of photographic silver halide emulsions is markedly improved, particularly with regard tofogging at elevated temperatures.

.Various salts and complexes of heavy metals including those of copper, cobalt and nickel have been added to photographic emulsions for purposes of toning and sensitization. However, applicant has found that the metal hydroxides are superior to the salts. The former have an extended stabilization effect. They areeffective over a wide range of concentration and do not have a deleterious action on other properties of photographic emulsions. This result is somewhat surprising in view of the fact that the water-soluble salts of nickel do not exhibit any significant stabilizing properties to a photographic emulsion. While copper nitrate has a slight stabilizing action, it must be used in .relatively small amounts, otherwise the sensitivity of the freshly prepared silver halide emulsion is markedly reduced. Copper chloride when added to a photographic emulsion in the amounts prescribed in the present application for copper hydroxide actually has a marked desensitizing action on photographic silver halide emulsions.

An economic advantage of the invention is that the cobalt, nickel and copper hydroxides can be obtained readily, in pure form, and they are relatively inexpen sive.

Another advantage of the invention is that, due to the fact that the copper, nickel and cobalt hydroxides are insoluble, there is no localized reaction at the point or portion of the emulsion Where the metal hydroxide is introduced. Ions are released slowly and this leads to more uniformly stabilized emulsions than it has been possible to obtain by means of water-soluble metal compounds.

Another advantage of this invention is that it provides a simple and effective process for improving the stability of photographic emulsions. The process is not only simple but uses economical and commercially available chemical compounds. Another advantage is that the process of stabilizing the emulsions can be practiced successfully by the ordinary technician and extreme care does not have to be exercised in the amount of metal hydroxide added since a relatively large amount still contributes stabilizing properties to the emulsion. Stabilization of the freshly prepared and coated emulsions, moreover, is accomplished Without any adverse effects on the optimum sensitivity of the freshly prepared emulsions, or emulsions which have aged, over a wide range of climatic conditions. The emulsions have high initial speed and good stability, that is, have relatively low fog values initially and upon aging.

I claim:

1. A process for stabilization of a photographic silver halide emulsion which comprises uniformly admixing with said emulsion an aqueous dispersion of finely divided particles of a Water-insoluble metal hydroxide take from the group consisting of cobalt, nickel and copper hydroxide in an amount sufiicient to introduce about 1.0 to about 30.0 moles of said hydroxide per 1000 moles of silver halide.

2. A process for the stabilization of a digested photographic Water-permeable colloid silver halide emulsion which comprises uniformly admixing with said emulsion an aqueous dispersion of finely divided particles of a Water-insoluble metal hydroxide taken from the group consisting of cobalt, nickel and copper hydroxide in an amount sufficient to introduce about 1.0 to about 30.0 moles of said hydroxide per 1000 moles of silver halide.

3. A process as set forth in claim 2 wherein said colloid is gelatin.

4. A process as set forth in claim 2 wherein said hyciroxide has a particle size of not more than microns in average diameter.

5. A process as set forth in claim 2 wherein said emulsion is a high speed silver iodobromide emulsion.

6. A water-permeable colloid silver halide photographic emulsion having uniformly admixed therethrough a water-insoluble metal hydroxide taken from the group consisting of cobalt, nickel and copper hydroxide in an amount sufficient to introduce about 1.0 to about 30.0 moles of said hydroxide per 1000 moles of silver halide.

7. A photographic emulsion as set forth in claim 6 wherein said hydroxide is in the form of particles having an average diameter from 1 to 8 microns.

8. A photographic emulsion as set forth in claim 6 wherein said colloid is gelatin.

9. A photographic element comprising a sheet support bearing at least one layer of a Water-permeable colloid silver halide photographic emulsion having uniformly admixed therethrough finely divided particles of a water-insoluble metal hydroxide taken from the group consisting of cobalt, nickel and copper hydroxide and having a particle size of 2 to 50 microns in an amount sufficient to introduce about 1.0 to about 30.0 moles of said hydroxide per 1000 moles of silver halide.

10. An element as set forth in claim 9 wherein said support is a hydrophobic film base.

References Cited in the file of this patent UNITED STATES PATENTS 2,284,877 Martinez June 2, 1942 2,584,030 Land Jan. 29, 1952 2,698,237 Land Dec. 28, 1954 

1. A PROCESS FOR STABILIZATION OF A PHOTOGRAPHIC SILVER HALIDE EMULSION WHICH COMPRISES UNIFORMLY ADMIXING WITH SAID EMULSION AN AQUEOUS DISPERSION OF FINELY DIVIDED PARTICLES OF A WATER-INSOLUBLE METAL HYDROXIDE TAKE FROM THE GROUP CONSISTING OF COBALT, NICKEL AND COPPER HYDROXIDE IN AN AMOUNT SUFFICIENT TO INTRODUCE ABOUT 1.0 TO ABOUT 30.0 MOLES OF SAID HYDROXIDE PER 1000 MOLES OF SILVER HALIDE. 